Electromagnetic actuator and control

ABSTRACT

An electromagnetic actuator includes a stator assembly mounted to a center pole formed of material having high magnetic permeability and functions as a return path for the magnetic field generated when current is passed through coils in the stator assembly. When current is applied to one or more coils within the stator assembly, a magnetic field is generated that interacts with a magnetic field generated by one or more magnets disposed within the armature assembly and causes the armature to move relative to the center pole thus, for example, opening or closing a valve.

CLAIM OF PRIORITY

This application is a continuation and claims priority of applicationSer. No. 10/810,538 of Thomas A. Froeschle, Roger Mark, Thomas C.Schroeder, Richard Tucker Carlmark, David E. Hanson, Jun Ma, andBenjamin G. K. Peterson entitled ELECTROMAGNETIC ACTUATOR AND CONTROL,which was filed on Mar. 26, 2004, and is incorporated here by reference.

TECHNICAL FIELD

This disclosure relates to electromagnetic actuators.

BACKGROUND

An internal combustion engine typically includes a number of cylindersthat each has a set of valves that open and close to allow fuel and airinto the cylinder and release exhaust from the cylinder. Typically, thevalves of an internal combustion engine are controlled mechanicallywith, for example, a cam shaft.

SUMMARY

In one aspect, the invention features an electromagnetic actuator thatincludes a center pole having a longitudinal axis and formed of amaterial having high magnetic permeability (e.g., a ferromagnetic orparamagnetic material). Coupled to the center pole is a stator assemblythat has an inner surface that defines an opening. A coiled conductor isdisposed near the inner surface of the stator assembly and is configuredto generate a first magnetic field when current is applied. The actuatoralso includes an armature assembly at least partially disposed withinthe stator assembly opening. A permanent magnet is disposed within thearmature assembly and moves in a direction parallel to a longitudinalaxis of the center pole when current is applied to the coiled conductorassembly. One advantage of having a center pole formed of materialhaving high magnetic permeability is that it allows the actuatorachieves a greater force output than a actuator with the same magneticcircuit without the center pole. Another advantage is that the centerpole also reduces the air gap of the flux loop for the magnetic circuit,thereby resulting in a more efficient magnetic circuit than one withoutsuch a center pole.

Various embodiments may include one or more of the following features.

The center pole may be formed of a plurality of segments. The centerpole also may act as a bearing surface for the armature assembly and maybe coated with a low-friction coating.

The permanent magnet of the armature assembly may be ring-shaped andradially magnetized and may be oriented such that the longitudinal axisdefined by the ring of the magnet is parallel (or coaxial) with thelongitudinal axis of the center pole. The permanent magnet of thearmature assembly may be split in the axial direction or formed ofmultiple segments (e.g., multiple arc-shaped segments) to interrupt thedominant eddy current path of the magnet.

The armature assembly may also include a valve stem that is adapted toopen or close a valve when current is applied to the coiled conductor.The center pole may define a channel in which a valve stem is at leastpartially disposed, thereby acting as a guide for the valve stem. Thevalve stem may be coupled to the remainder of the armature assembly suchthat the valve stem has freedom of movement in directions perpendicularto the longitudinal axis of the center pole and/or freedom of to rotatearound the longitudinal axis of the center pole. The valve stem may havea ball-shaped tip formed at one end that fits into a ball cage attachedto the armature assembly such that the valve stem is secured to theremainder of the armature assembly in a direction parallel to thelongitudinal axis of the center pole.

The stator assembly may include a plurality of coils that are configuredsuch that adjacent coils generate magnetic fields of opposite polarity.For example, the plurality of coils may be connected in series and maybe wound such that adjacent coils are wound in opposite directions.Alternatively, adjacent coils may be wound in the same direction andconfigured to receive current with opposite relative polarity. Thearmature assembly may also include corresponding number of permanentmagnets that are arranged such that adjacent permanent magnets haveopposite polarity. Spacers may be disposed between each of the permanentmagnets and the magnets and/or spacers may be split in the axialdirection to interrupt dominant eddy current paths.

The stator assembly may also include one or more back iron membersformed of a material having high magnetic permeability, and the innersurface of the stator assembly is coated with a dielectric material.

The actuator may employ an overhung magnet design in which the axialheight of a magnet (i.e., the height of the magnet as measured relativeto the longitudinal axis of the center pole) is greater than the axialheight of a corresponding coiled conductor in the stator assembly.Similarly, the actuator may employ an underhung magnet design in whichthe axial height of a magnet is less than the axial height of acorresponding coiled conductor in the stator assembly.

The actuator may be configured such that the force of the armature as afunction of displacement of the armature relative to the stator assemblyis substantially constant over an intended range of excursion. Theactuator may be configured such that the detent force profile of theactuator as a function of displacement of the armature relative to thestator assembly is substantially zero over an intended excursion rangeof displacement.

The actuator may be configured to form part of a cooling circuit and mayinclude a cooling jacket that is disposed at least partially around thestator assembly and circulates cooling fluid. The center pole may alsoinclude one or more channels that are configured to circulate coolingfluid.

The actuator may be configured to open and close a valve and acontroller may be electrically connected to the actuator to control theoperation of the actuator. The controller may be configured to receiveinformation about one or more operating states of the valve (e.g., valvevelocity, acceleration, and/or position) and apply a control signal tothe coil(s) based on the received information to generate a magneticfield that causes the armature assembly to move relative to thelongitudinal axis of the center pole. The controller may receiveinformation about both the velocity and position of the valve andselectively apply a velocity feedback control and a position feedbackcontrol to position the valve.

In another aspect, the invention features a method for controlling anelectromagnetic valve actuator having a stator that defines alongitudinal axis and an armature disposed within the stator thatincludes receiving information about velocity and position of the valveand applying a control signal to the actuator by selectively activatinga velocity feedback loop and a position servo feedback loop to positionthe valve to a desired position.

Various embodiments may include one or more of the following features.The velocity feedback loop may function to reduce the valve velocity.The desired position of the valve may be where the valve is fully openor fully closed. The method may also include activating the velocityfeedback loop to compensate for detent force at a given armaturedisplacement.

In another aspect, the invention features an internal combustion enginethat includes a cylinder that defines a chamber, a valve adapted tocontrol the flow of a liquid or a gas into or out of the chamber, and anelectromagnetic actuator coupled to the valve to control operation ofthe valve. The actuator includes a stator assembly having an innersurface that defines an opening and a coiled conductor disposed near theinner surface and a center pole formed of a material having highmagnetic permeability (e.g., paramagnetic or ferromagnetic material) anddefining a longitudinal axis. The actuator also includes an armatureassembly at least partially disposed within the stator assembly openingand moves in a direction parallel to a longitudinal axis of the centerpole when current is applied to the coiled conductor assembly.

Various embodiments may include one or more of the following features.The internal combustion engine may also include a controller configuredto receive information about one or more operating states of the valve(e.g., valve velocity, acceleration, and/or position) and apply acontrol signal based on the received information to the coil to generatea magnetic field that causes the armature assembly to move relative tothe longitudinal axis of the center pole. The controller may receiveinformation about both the velocity and position of the valve andselectively applies a velocity feedback control and a position feedbackcontrol to position the valve.

The internal combustion engine may further comprise a cooling circuitthat includes a heat exchanger and a pump that circulates cooling fluidbetween the electromagnetic actuator and the heat exchanger. Theelectromagnetic actuator may also includes a cooling jacket disposed atleast partially around the stator assembly and having one or morechannels that circulate cooling fluid between the electromagneticactuator and the heat exchanger. The electromagnetic actuator may alsoinclude one or more channels within the center pole that circulatecooling fluid between the electromagnetic actuator and the heatexchanger.

An electromagnetic actuator designed in accordance with the teachings ofthis disclosure may be employed in an internal combustion engine tovariably and independently control the engine's intake and exhaustvalves. One advantage of using an actuator in an engine is that ispermits an engine to start without the need of a secondary motor (e.g.,a starter motor). Another advantage of using such an actuator in anengine is that it may improve engine emissions by stopping the enginewhen it would otherwise be idling (e.g., while a vehicle is stopped at atraffic light).

While the electromagnetic actuators described below are described in thecontext of an internal combustion engine, it should be understood thatthe teachings of this disclosure are not meant to be limited to valvecontrol in an engine, but rather may be applied to a wide variety ofapplications.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram of an internal combustion engine.

FIG. 1B is a diagram of a chamber in an internal combustion engine.

FIGS. 2A-2H are diagrams of an electromagnetic actuator.

FIG. 3A is a diagram of a cooling circuit for an electromagneticactuator.

FIG. 3B is a diagram of a cooling jacket for an electromagneticactuator.

FIG. 3C is a diagram of a actuator with a cooling conduit through thecenter pole.

FIG. 4A-4I are diagrams of another electromagnetic actuator.

FIG. 5A is a graph illustrating simulated acceleration vs. positionprofile for an overhung and underhung magnet design.

FIG. 5B is a graph illustrating simulated force vs. position profilesfor an overhung and underhung magnet design.

FIG. 5C is a graph illustrating simulated detent force characteristicsfor an overhung and underhung magnet design.

FIG. 6 is a diagram of a control system for electromagnetic actuators.

FIG. 7 is a block diagram for a closed-loop control system for anelectromagnetic actuator.

FIG. 8 are two graphs showing the relationship between control currentapplied to a set of stator coils and the displacement of an armature inone embodiment of an electromagnetic actuator.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As shown in FIG. 1A, an internal combustion engine 1 includes a numberof cylinders, e.g., 2 a-2 b, that each houses a piston, e.g., 4 a-4 b.Each of the pistons, in turn, is mechanically connected to crankshaft 5with a rod, e.g., 6 a-6 b. Each cylinder, e.g., cylinder 2 a, as shownin FIG. 1B, includes an intake valve 9, exhaust valve 9′, spark plug 7,and fuel injector element 10 each disposed at least partially within achamber 11 of the cylinder. A control unit (not shown) controls theintake and exhaust valves 9′, 9 by controlling intake valve actuator 8and exhaust valve actuator 8′, respectively. The control unit alsocommands the fuel injector to inject a suitable amount of fuel-airmixture into the chamber 11, ignites the fuel-air mixture at theappropriate time with spark plug 7, and then vents the exhaust from thecombustion of the fuel-air mixture through exhaust valve associated withvalve actuator 8. The control unit may control the operation of thevalves, fuel delivery and spark plug ignition in accordance with themethods described in a patent application titled “Controlled Startingand Braking of an Internal Combustion Engine” by David Hanson, Jun Ma,Benjamin G. K. Peterson, and Geoffrey Coolidge Chick, filed concurrentlywith this application, which is fully incorporated by reference.

Each valve actuator, e.g., valve actuator 8 shown in FIG. 2A, includesan armature assembly 14 disposed within a stator assembly 12. Uponactuation, the armature assembly 14 slides along the longitudinal axis Aof the stator assembly 12 to open (or close) a valve (not shown in FIG.2A).

As shown in FIG. 2B, the stator assembly 12 includes an outer housing 29that is mounted to a center pole 28. The center pole 28 is a hollow,tube-like structure that extends beyond the outer housing 29 and acts asa guide for a valve stem (shown in FIGS. 2G-2H) attached to the armatureassembly. In addition to acting as a guide for the valve stem, thecenter pole is formed of a material having high magnetic permeabilityand provides a magnetic return path for the magnetic field generatedwhen current is passed through the coil conductor assembly 23. Acoupling flange 30 mechanically couples the center pole 28 and outerhousing 29.

The outer housing 29 includes a coil conductor assembly 23 surrounded byinterlocking back iron members 24. A series of screws, e.g., 27 a-27 b,through a cap 26 secures the interlocking back iron members in place. Inthis particular implementation, the coil conductor assembly 23 includestwo pairs of round copper wire coils 20 and 22 that are wound inopposite directions (e.g., coils 20 are wound clockwise and coil 22 arewound counter-clockwise, or visa versa) and connected in series suchthat when a current from a single drive circuit is applied to the coils,the coils produce magnetic fields of opposite polarity. In other words,one pair of coils (e.g., coils pair 20) will produce a magnetic field ofone polarity and the second pair of coils (e.g., coil pair 22) willproduce a magnetic field of the opposite polarity when a current isapplied to the coils. The two pairs of coils are alternately arrangedwithin the stator assembly such that the coils that form a pair (e.g.,coil pair 20) are not adjacent to one another. As will be explained inmore detail below, the alternatively wound coils 20, 22 are aligned withmagnets of alternating relative polarity in the armature. When currentis applied to the coils 20, 22, a magnetic field is formed between theouter housing and the center pole which causes the magnetized armatureto slide along the longitudinal axis A of the actuator. The alternatingpolarity of neighboring coils and magnets work as magnetic flux returnpaths for each other.

In another implementation, all of the coils of the coil conductorassembly are wound in the same direction and are supplied with separatecurrent signals of alternating polarity to produce a series ofalternating magnetic fields. Other implementations may employ one ormore coils that produce magnetic fields of opposite polarities or of thesame polarity. The coils 20, 22 may be constructed from a conductor(e.g., wire or conductive tape) having a variety of cross sectionalshapes such as circular, elliptical, rectangular or square.

As shown in FIG. 2C, each back iron member 24 is comprised of threecircumferential segments 25 a-25 c. The use of separate circumferentialsegments allows for radial thermal expansion of the copper coils aselectrical power is applied thus reducing the risk of fracture of theback iron members 24. The back iron members 24 directs the magneticfield produced by the electrical conductors towards the armatureassembly, while the center pole 28 advantageously serves as a returnpath for the magnetic circuit generated when current is passed throughthe coils. By having a center pole act as a magnetic return path for themagnetic circuit, the actuator achieves a greater force output than aactuator with the same magnetic circuit without the center pole. Thecenter pole also reduces the air gap of the flux loop for the magneticcircuit, resulting in a more efficient magnetic circuit than one withoutsuch a center pole. In order for the center pole 28 to act as a magneticreturn path, it should be formed of a material having high magneticpermeability, such as ferromagnetic or paramagnetic material.

Ferrous elements of the stator assembly 12, including the center pole 28and back iron members 24, are preferably constructed of materials havinghigh magnetic permeability and high magnetic saturation characteristics.It is also preferable to use materials that have high electricalresistivity in order to reduce the dynamic losses of the ferrouselements. Materials such as silicon iron alloys or soft magneticcomposites provide high magnetic permeability and saturationcharacteristics and are also highly resistive and may be used to formthe center pole 28 or other ferrous elements of the actuator.

In a preferred implementation, the back iron members 24 and center pole28 are formed of a powdered metal Soft Magnetic Composite (SMC) material(such as SM2 or SM3 made by Mii Technologies, LLC, headquartered at WestLebanon, N.H., or Somaloy™ 500 made by Hoganas, headquartered atHoganas, Sweden), which has a combination of high electrical resistivityand high magnetic permeability.

The center pole 28 may be formed as a single piece construction (asshown in FIG. 2B) or it may be compositely formed from a number ofsegments of homogeneous or heterogeneous material. Forming the centerpole 28 from discrete segments will increase the electrical resistivityof the center pole 28 over a single-piece construction and lower itssusceptibility to eddy currents.

The coupling flange 30, which provides a mechanical connection betweenthe stator and center pole, and the cap 26, which secures the back ironmembers in place, are preferably made a non-magnetic, resistive materialwith lower susceptibility to eddy currents such as austenitic stainlesssteel.

The stator assembly is preferably coated with a potting epoxy or otherhigh strength, high dielectric adhesive material, which helps to bothsecure the coils within the stator assembly, protect the coils fromphysical wear and provide electrical insulation to the back iron members24. The potting epoxy may be applied via an assisted impregnationprocess, in which the actuator and surrounding fixtures are placed in avacuum environment with the potting epoxy introduced via an inlet tubewith an overflow tube to indicate a completed fill.

In another implementation, the inner surfaces of the back iron membersare coated with a dielectric material to provide electrical insulationfor the actuator. One technique for coating the inner surfaces of theseparts is to first electro coat the surfaces with approximately 0.001inches of dielectric paint followed by a coat of approximately0.002-0.004 inches of epoxy-based powder-coat. This technique providesredundant protection against voltage breakdown between coils and thestructures that the coils may come into contact. In addition to coatingthe inner surfaces of the back iron members, the entire inner surface ofthe stator assembly may be coated with a high dielectric strengthpotting epoxy or film material, such as a thin Kapton® polyimide film(made by DuPont High Performance Materials headquartered in Circleville,Ohio) bonded to the surface. This layer of material provides electricalinsulation between the outer surface of the armature assembly and theinner surface of the stator assembly and also serves as a physicalbarrier between the inner surface of the stator assembly 12 and anycooling fluid, such as engine oil, to which it may be exposed.

In addition, the center pole is also preferably coated with a lowfriction protective coating, such as an electroless nickel coating, toimprove the bearing and wear qualities of the armature and statorassembly as the armature slides along the center pole during use.

Referring to FIGS. 2D-2F, the armature assembly 14 includes two pairs ofpermanent magnets 32, 34, that are radially magnetized, that is themagnets have a first polarity along the inner circumference of themagnet and a second polarity along their outer circumference. In oneimplementation, as shown in FIG. 2F, one pair of magnets have asouth-north polarity (e.g., magnet pair 32) while the second pair has anorth-south polarity (e.g., magnet pair 34). Like the pairs of coils inthe stator assembly 12, the two pairs of magnets are alternativelyarranged within the armature assembly 14 such that the magnets that forma pair (e.g., magnet pair 34) are not adjacent to one another. While theradial cross-section of the magnets is shown as having a circularcross-section in the exemplary design, other implementations may usemagnets having other cross-sectional shapes.

Referring to FIG. 2D, the armature assembly 14 includes magnet spacers36 interposed between adjacent magnets and a series of clips 40 thatcouple adjacent spacers 36 thus securing the magnets 32, 34 in place.The magnetic spacers 36 are preferably formed of a high modulus, lowdensity material having a high resistivity, such as titanium. In thisimplementation, the clips 40 provide a bearing surface for the innerdiameter of the armature assembly and may be coated with a low frictioncoating, such as diamond-like carbon (DLC) coating. In anotherimplementation, the inner and outer diameters of the spacers may extendslightly beyond the inner and outer diameters of the magnets in orderbear the frictional load during operation. In this implementation, thebearing surfaces of the spacers are preferably coated with a lowfriction coating (e.g., DLC, molybdenum disulfide).

Each of the magnets 32, 34 and the spacers 36 are split in the axialdirection to interrupt the dominant eddy current path which helps toreduce dynamic losses. Other implementations may use magnets and/orspacers that are formed of multiple arc segments, which creates multiplediscontinuities in the dominant eddy current path for each element.Although four magnets and coils are shown, other implementations mayemploy various numbers and combinations, both in arrangement andmagnetization, of these parts.

The armature assembly 14 also includes a ball joint assembly 38 and acoupler 42 that couples the valve stem assembly 50 to the remainder ofthe armature assembly 14. A number of clips 40 attach the coupler 42 tothe rest of the armature assembly 14. The clips 40 may be furtheradhered to the spacers 36 and to coupler 42 using an adhesive, such asan epoxy-based adhesive.

Referring to FIG. 2E, the ball joint assembly 38 includes a ball cage 45and a valve stem assembly 50, which includes an upper stem 46 and alower stem 48. One end of the upper stem 46 has a ball shape 44 whilethe other end has a male thread (not shown). The ball shape end of theupper stem 46 fits into the ball cage 45, and the male threaded end ofthe upper stem 46 threads into a mating female thread in the lower stem48. The ball joint assembly 38 functions to couple the armature 14 tothe valve stem 50 in the axial direction but leaves other directions,such as the two other translational directions and the three rotations,uncoupled. Other implementations may use other mechanical assemblies tocouple the valve stem to the remainder of the armature assembly in whichsome directions are coupled and other directions are uncoupled to avoidoverconstraining the mechanical assembly.

Using permanent magnets paired with the coils and ferrous elements ofthe stator assembly 12, the two magnetic sources operate to move thearmature assembly 14 in a linear motion within the stator. As discussedbefore, similar to the coil conductor assembly, the radially magnetizedadjacent magnets are oppositely polarized. Other elements of thearmature are non-motion producing, and serve to create axial spacing ofthe magnets as well as provide mechanical coupling between the magnetsand the valve stem. The axial spacing of the magnets and coils depend onthe intended excursion of the design and the desired positionalrelationship between the axial height of the coil and magnet. Ingeneral, the top and bottom of each magnet will stay within the axiallocation (defined as the distance of the coil, measured in the axialdirection, from the bottom to the top of the coil) of its mating coiland back iron material at the extreme ends of travel for the mostconstant force output over that excursion.

When current is applied to the coils of the stator assembly 20, 22, themagnetic field produced by the coils causes the armature assembly 14 tomove, in an upward or downward direction (relative to FIG. 2A). As anexample, if the armature magnets have a polarity as indicated in FIG. 2Fand current flows in a clockwise direction through coils 20 and in acounter-clockwise direction through coils 22, the armature assembly 14will move in a downward direction. Referring to FIG. 2H, as the armatureassembly 14 moves downward, the valve stem 50 pushes the valve 37 to afully opened position. Similarly, as shown in FIG. 2G, when current isreversed, the armature assembly 14 is pulled upwards, causing the valvestem to pull the valve against the valve seat 39, thus closing thevalve.

The slide of the armature assembly 14 against the center pole 28provides a substantial thermal path to the magnets 32, 34 which may leadto demagnetization. Thus, the choice of material for the magnets 32,34is a balance between the desire for a high energy product to providehigher actuator force output and the stability of the magneticproperties. In a preferred implementation, neodymium-iron-boron magnetsare selected for their energy density and ability to be radiallymagnetized. High coercive force characteristics are important for thestability of the material in the presence of demagnetizing influencessuch as externally applied magnetic fields and high temperatures. Otherembodiments may use magnets formed of a permanent magnet materialcomposition incorporating a rare earth metal, such as Neodymium orSamarium Cobalt. Examples of other suitable materials include Nd35s,Nd38s, Nd42s and Nd30s, made by Hitachi Magnetics Corporation,headquartered at Edmore, Mich.

In addition to heat generated by friction, eddy currents induced by therapid changes in magnetic flux density generate additional heat energy.As previously mentioned, the center pole and back iron members may beformed of a number of arc-shaped segments, which interrupt the dominanteddy current path. Also, selection of materials having both highmagnetic permeability and high electrical resistivity, such as SMC orSomaloy 500 material, can be used to form the center pole and back ironmembers in order to further reduce dynamic losses. In addition to thesetechniques, an actuator may also include a cooling system to activelycool the actuator during use.

For example, as shown in FIG. 3A, a cooling system 51 includes a pump 53that circulates cooling fluid, such as water, 50/50 ethyleneglycol/water mix, engine oil or other cooling fluid, between a heatexchanger 55 and one or more actuators 57 to transfer heat away from theactuator(s). One technique for circulating cooling fluid within anactuator is by placing a cooling jacket, such as cooling jacket 52 shownin FIG. 3B, around the outer surface of the stator assembly (not shown)to form part of the cooling circuit. A material having high thermalconductivity, such as thermal grease, potting compound with high thermalconductivity, thermally conductive elastomers or thermally conductiveadhesive tapes, may be used to eliminate air gaps between the coolingjacket 52 and the stator assembly. The cooling jacket 52 may beconnected to pump 51 and heat exchanger 55 to form a cooling circuit.

Other implementations may use other known cooling systems, such as aheat pump, to remove heat from the actuator. In a vehicle application,air flow arising from motion of the vehicle may be directed over theactuators to provide forced convection cooling. Auxiliary fans couldalso be used.

A cooling circuit may also be formed within the center pole of anactuator. For example, as shown in FIG. 3C, a thin-walled conduit may bedisposed within a bore formed in the center pole 63. Pump 51 (shown inFIG. 3A) may circulate cooling fluid through the conduit 61 in thecenter pole and a heat exchanger 55 to transfer heat away from thecenter pole.

A cooling system may be an independent cooling system, or may be part ofa cooling system already present in the application in which theactuator is used. For example, if an actuator is used to control anintake, exhaust or fuel injection valve in an internal combustionengine, the engine may be designed such that the cooling system alsocools the actuator by, for example, circulating cooling fluid through acooling jacket and/or a conduit disposed in the center pole. By coolingthe actuator with the engine's cooling system, there is no need for aseparate heat exchanger or pump. However, in some applications, it maybe desirable to have greater control over the temperature of theactuator and, thus an independent cooling system may be employed for oneor more actuators. For example, individual actuators may have their ownindependent systems, or the same cooling fluid may flow through multipleactuators, which connect to a central heat exchanger.

For an on-engine application, it is desirable to thermally isolate theactuator from the engine block to the actuator in order to heat exchangefrom the engine block to the actuator. In this regard, a thermalinsulator formed from a low thermal conductivity material such as aceramic or high-temperature plastic may be placed between the actuatorand the engine block.

It is also desirable to thermally isolate the valve stem (which isexposed to combustion in the engine's cylinders) from the remainder ofactuator. In this regard, the valve stem is preferably formed of amaterial having low thermal conductivity, such as titanium.

As shown in FIGS. 4A-4G, another embodiment features an actuator 60 thatincludes a stator assembly 62 having a coil assembly with three coils 64a-64 c and an armature assembly 66 having three corresponding radiallymagnetized permanent magnets 68 a-68 c. The coils 64 a-64 c areconfigured such that adjacent coils will generate magnetic fields ofopposite polarity. In this implementation, the coils 64 a-64 c areconnected in series and the uppermost and lowermost coils, i.e., coils64 a and 64 c, are wound in one direction (e.g., clockwise) and thecoils located in the middle of the stator assembly, i.e., coils 64 b,are wound in the opposite direction (e.g., counter-clockwise). Thus,when current is applied to the coils, adjacent coils generate magneticfields having opposite polarities. The coils in this implementation areformed of round copper wire, however, other implementations may form thecoils from conductive tape or wire having different cross-sectionalareas or shapes.

The magnets 66 a-66 c of the armature assembly 64 are configured suchthat adjacent magnets have opposite radial magnetization. In otherwords, the uppermost and lowermost magnets, i.e., 66 a and 66 c, have afirst radial polarization (e.g., north-south) whereas the magnet locatedin the middle of the armature assembly, i.e., magnet 66 b, has anopposite radial polarization (e.g., south-north). In thisimplementation, the actuator 60 uses an overhung design in which theaxial height of the magnets, 66 a-66 c, is larger than the axial heightof the corresponding coils, 64 a-64 c.

Referring to FIG. 4B, the stator assembly 62, in addition to includingthe three coils 66 a-66 c, also includes a center pole 70 and a seriesof interlocking back iron members 72. The center pole 70 is formed of amaterial having high magnetic permeability (e.g., SMC) and functions asa magnetic return path for the magnetic field generated by the coils.

The stator assembly also includes a finned housing 76 that secures theback iron members 72 in place, and a coupler 78 that secures the finnedhousing 76 to the center pole 70. Several screws disposed in holes 79mechanically couple the finned housing 76 to the coupler 78. The finnedhousing is preferably made of a material having high thermalconductivity, such as aluminum, which helps to draw heat away from theback iron members 72 and coils 64 a-64 c. Air flow may be directed overthe fins to help transfer heat away from the actuator 60.

As shown in FIGS. 4C-4D, the adjacent back iron members 72 are formed ofthree arc segments, e.g., 74 a-74 c, that advantageously interrupt thedominate eddy current path and thus reduce dynamic losses. In thisimplementation, the center pole 70 and back iron members 72 are formedof powdered metal Soft Magnetic Composite (SMC) material (such as SM2 orSM3 made by Mii Technologies, LLC, headquartered at West Lebanon, N.H.,or Somaloy 500 made by Hoganas, headquartered at Hoganas, Sweden). Otherimplementations may form the center pole and back iron members fromother materials having high magnetic permeability, and preferably, highelectrical resistivity.

As shown in FIGS. 4E-4F, the armature assembly 64 includes two spacers82 a-82 b disposed between the three radially magnetized magnets 66 a-66c. The armature assembly also includes a ball joint assembly 86 thatmechanically connects a valve stem 88 to the remainder of the armatureassembly. A series of screws disposed in holes 89 a-89 d secures theball joint assembly 86 to a coupler 90. One or more clips, e.g., clip92, mechanically secures the magnets 66 a-66 c and spacers 82 a-82 b tothe coupler 90. The magnets 66 a-66 c and spacers 82 a-82 b are split 83a, 83 b in their axial direction to interrupt the dominant eddy currentpath.

Referring to FIG. 4F, the valve stem 88 includes a ball 94 at one endthat is secured within the ball joint assembly 86 such that the valvestem is secured along the longitudinal axis of the armature assembly,but is free to move in other directions.

When current is applied to the coils, the magnetic field produced by thecoils causes the armature assembly to move, in an upward or downwarddirection. As shown in FIG. 4H, when current flows through the coils inone direction, the armature assembly 66 moves downward, causing thevalve stem 88 to pushes the valve 87 to a fully opened position.Similarly, as shown in FIG. 4G, when current is reversed, the armatureassembly 66 is pulled upwards, causing the valve stem 88 to pull thevalve against the valve seat 91, thus closing the valve. Note that inthis implementation, the center pole does not act as a guide for thevalve stem.

As shown in FIG. 41, a spacer 96 is disposed within the center pole 70to limit the excursion range of the armature. In this implementation,the spacer 96 is a Belleville spring washer, however otherimplementation may use springs or elastomeric or polymeric elements tolimit the range of travel of the armature. In an on engine application,limiting the peak excursion of the armature may be desired to avoidinterference between a piston and a valve controlled by the actuator.

Maximum displacement, the force versus displacement profile and detentforce profile of the actuator is achieved by selecting appropriatedesign parameters such as the coil topology, relative height andpositional relationship of magnets and coils, back iron and center poledimensions and materials, and coil materials. Additionally, operation ofthe actuators may be controlled through the magnitude, duration andpolarity of current applied to the coils, thus permitting flexiblecontrol of the valve's operating parameters such as the valve lift(i.e., the amount the valve is open) and valve timing (i.e., the openingand closing points of the intake and exhaust valves with relation to thecrankshaft position).

In one embodiment, an actuator may employ an underhung magnet design inwhich the axial height of the coils is larger than the height of themagnets. In one specific underhung magnet design using four coils andfour magnets, each turn of the coil is made of copper. Each coiloccupies a volume bounded by inner (ID) and outer diameters (OD) of 1.56inches and 2.03 inches, respectively, and a height of 0.7 inches. Theratio of magnet height to the radius of the magnet cross section isabout 3.6:1 with inner and outer diameters of 1.31 inches and 1.53inches, respectively, with a height of 0.4 inches. Each magnet is formedof NdFeB (specifically, Nd HS35AR made by Hitachi Magnetics Corporation,headquartered at Edmore, Mich.) and has a mass of roughly 25 g.

In another embodiment, an actuator may employ an overhung magnet designin which the axial height of the coils is less than the height of themagnets. In one implementation, an actuator uses an overhung magnetdesign with three copper coils and three magnets. Each of the coils hasinner and outer diameters of 1.48 inches and 2.28 inches respectively,and a height of 0.4 inches. Each of the magnets has inner and outerdiameters of 1.24 inches and 1.44 inches respectively and a height of0.8 inches. The ratio of magnet height to the radius of the magnet crosssection width is 8.1:1. Each magnet is formed of NdFeB (specifically, NdHS30FR made by Hitachi Magnetics Corporation, headquartered at Edmore,Mich.) and has a mass of about 39 g.

One way to assess the performance of an actuator design is to plotacceleration versus displacement of an actuator. The acceleration is thenormalized force per unit moving mass, defined as magnetostaticforce/moving mass (where moving mass is made up of the magnet mass plusapproximately 100 grams of parasitic mass in an exemplary embodiment).Parasitic mass refers to any non-force producing moving mass (i.e. anyportion of the moving mass in the exemplary embodiment that is notpermanent magnet material) such as the valve, magnet spacers, coupler,ball joint assembly, sensors, etc. FIG. 5A plots the acceleration versusdisplacement profile of simulated actuator having the overhung (line A)and underhung (line B) designs described above using Maxwell® v.9.0.19available through ANSOFT Corporation (www.ansoft.com). The simulationresults shows that the overhung design has an approximately linearacceleration over an intended excursion range of between −0.15 inchesand +0.15 inches from center. The horizontal axis represents the rangeof positions from valve fully closed (−0.2 in) to valve fully open (0.2in).

FIG. 5B shows simulated force versus displacement profiles for theexemplary overhung (line A) and underhung (line B) designs describedabove using, also using ANSOFT's Maxwell® v.9.0.19 software. The forcevariation shown for the overhung design is substantially constant, overan intended excursion range between −0.15 inches and +0.15 inches fromcenter, which is 75% of the maximum range of travel.

A substantially constant force output and acceleration over the intendedexcursion range is advantageous because it simplifies the control schemeneeded to control actuator displacement and enables variable lift, whichcan be particularly useful when actuators are used to actuate the intakeand exhaust valves in an internal combustion engine.

Referring back to FIG. 2A, a detent force results from the magneticattraction between the ferrous elements of the stator, such as the backiron members 24 and center pole 28, and the magnets 32, 34 in thearmature assembly when the stator is not energized. In a preferredembodiment, an actuator is configured such that when the armatureassembly moves to the valve-fully-closed position, the detent force actsin the seating direction thus assisting to bring the valve 37 (shown inFIGS. 2G-2H) to its seat. In such an embodiment, the detent force isalso advantageously used to keep the valve closed after it is seated. Byusing the detent force as a biasing force, a control system preferablydoes not need to supply current to the coils to keep the valve closed,which, in a four-cycle internal combustion automobile engine isapproximately two-thirds of the cycle time.

FIG. 5C compares the detent force characteristics for the previouslydescribed underhung (line B) and overhung (line A) magnet designs. Theunderhung magnet design exhibits more substantial detent force at theextreme ends of travel (i.e., between −0.2 and −0.15 inches and between+0.15 and +0.2 inches), which aids the force output at one end oftravel, but subtracts at the other end. The overhung magnet designexhibits the same trend with its detent force, but has a larger regionof substantially zero detent force over the intended excursion range.The magnetic detent force profile of the actuator also depends on theselection of various design parameters such as coil materials, coilvolume, magnet material, magnet volume, back iron material andconstruction, and center pole material and construction.

Referring to FIG. 6, a control system 506 for controlling a plurality ofintake and exhaust valve actuators in an internal combustion automobileengine includes an upstream control processor 500, and a series ofdownstream control processors 501-503 that are each dedicated to aparticular intake or exhaust valve.

Upstream control processor 500 receives crankshaft position information505 (which may be fed from an optical encoder or other device thattracks crankshaft position) and control instructions from a centralcontroller, such as an electrical engine control unit (ECU) 504. Theupstream processor uses this received information to generate andtransmit to the downstream processors 501-1, 501-2 . . . 501-N signalsthat indicate the valve timing (i.e., the opening and closing points ofthe intake and exhaust valves with respect to the crankshaft position)and valve lift (i.e., the amount the valve is open) for each of thecontrolled valves.

As described more fully in the patent application titled “ControlledStarting and Braking of an Internal Combustion Engine” by David Hanson,Jun Ma, Benjamin G. K. Peterson, and Geoffrey Coolidge Chick, filedconcurrently with this disclosure, the valve timing and valve liftparameters for specific operating modes (e.g., the self-starting orengine braking modes are described in the above references application)may be determined dynamically through a closed-form calculation.Alternatively, the valve parameters may be determined statically throughuse of a look-up table where pre-calculated valve timing and valve liftparameters corresponding to different operating modes have been storedin memory. In the static implementation, the upstream processor 500searches through a set of pre-calculated look-up tables corresponding tothe different operating modes based on instructions received from ECU504.

The downstream control processors 501 receive a valve control signalsfrom the upstream processor, which may be in a variety of forms such asa digital pulse. In response to receiving a valve control signal fromthe upstream processor, the downstream control processor issues avoltage signal to a voltage controlled pulse-width modulated (PWM) powermodule 502 to produce an output driving current of a certain magnitudeand polarity. The PWM power module 502 then supplies the current signalto the coils of the valve actuator 503. The magnitude and polarity ofapplied current determine the opening and closing behavior of the intakeor exhaust valve actuator 503. Downstream control processors (e.g. 501-1for valve actuator 503-1) control also receive feedback information onone or more operating states of the valve (i.e., acceleration, velocity,and/or position) and adjust the control signal to the PWM based on thecurrent valve state information.

Valve states can be monitored via one or more sensors mounted on thevalve and/or actuator. For example, valve actuator velocity (V) anddisplacement (lifting, L) can be determined by a positional sensor suchas an optical encoder. The sensor may measure velocity or displacementdirectly and calculate the other quantity as needed using adifferentiator or integrator to determine the other quantity. In the oneimplementation, a Linear Velocity Transducer (LVT) is used to measurevelocity directly, and is mounted on the top of the armature.Alternatively, an accelerometer could be used.

It should be understood that processors such as 500 and 501-1 arefunctional blocks which may reside in one or more physical modules andmay be in the form of hardware, software or any combination of hardwareand software, or in analog or digital form.

As said, downstream processors (e.g. 501-1) control the dynamics of eachindividual valve by controlling the magnitude and polarity of currentapplied to the actuator. There are many ways of implementing such acontrol strategy. FIG. 7 shows one embodiment of a feedback basedcontrol strategy to implement the function of downstream processor501-1.

As shown in FIG. 7, the downstream processor 501-1 can issue voltagecommands 604 and 605 to the PWM power module that would cause the PWMmodule to provide full current (positive or negative) to the actuators.Input voltage commands 604 and 605 are synchronized with the rising orfalling edge of a valve timing signal received from the upstreamcontroller, which triggers valve opening or closing. The downstreamprocessor also includes a velocity feedback loop 601 that controls thevelocity of the armature (typically used in a negative feedback mode toreduce the velocity of the armature), and a position servo(displacement) feedback loop 602 that fine-tunes the valve displacementto a desired position. The downstream controller also includes aswitching mechanism 603 that receives the valve lift and timinginstructions from the upstream processor as well as valve stateinformation. The switching mechanism uses this information, as well asthe detent force profile of the actuator (which is stored in the memoryassociated with the processor) to selectively activate and deactivatepositive or negative full current commands, the velocity feedback loopand the position servo (displacement) feedback loop, to control valveopening and closing.

Referring to FIG. 8, valve displacement (graph 700) and a correspondingcurrent control signal (graph 702) are plotted as a function of timeusing the exemplary control system described in FIGS. 6-7.

When a downstream processor senses the rising edge of a valve controlsignal received from the upstream processor at time T(0), it triggersthe valve actuator to open by issuing a full positive current controlvoltage command 703 to PWM power module 502-1 (identified as point (a)in FIG. 8). When the armature reaches a point where the distance D(1)and velocity satisfy a predetermined equation, which occurs at timeT(1), switching mechanism 603 of the downstream processor switches tointroduce negative velocity feedback signal 705 (and disables thepositive full current command) which introduces a control current signalwith reverse polarity to slow the armature down. The predeterminedequation relationship between valve velocity V(1) (at time T(1) beforeactivating negative velocity feedback) and stopping distance (which isdefined as the displacement difference between valve lift D(1) at timeT(1) and the desired displacement position D(3) at time T(3)), can berepresented approximately as a linear relationship (ignoring factorssuch as engine chamber pressure). Based on V(1), D(1), D(3) and thelinear relationship, the negative velocity feedback loop 601 can beselectively activated and timely controlled via switching mechanism 603to stop the valve at time T(2).

Ideally point (c) will match point (d). That is, at time T(2) the valvewill have stopped exactly at a desired position. However, in realapplications, the physical plant changes from time to time, and valvedynamics are influenced by disturbances associated with cylinderrespiration. As a result of the disturbances, the armature may slow to astop at a location (c) which is close to the desired location (d) butmay not be exactly at position (d), as the magnitude of the appliedcontrol current is reduced to zero (by the negative velocity feedbackloop). The servo displacement loop 602 is then selectively activated bythe switching mechanism 603 to replace the velocity feedback loop. Theposition servo control generates a current signal for fine-tuning valveposition, to accurately push the valve to the desired position (d) attime T(3). It will also maintain its position there until a valvelanding signal is received. In the illustrated example, the desireddisplacement position is the expected valve lift. It should be notedthat the expected displacement position could be less than the maximumlift (for example, ⅔ of the maximum lift). D(2), which is thedisplacement at time T(2), may be larger or smaller than D(3) (thedesired displacement) after the velocity feedback loop is deactivatedand there may be small oscillations during the course of settling frompoint (c) to point (d). The corresponding position servo control currentmay also oscillate between positive and negative values. The exactbehavior depends on the dynamics of the position servo control loop.

For a valve closing event, it is desirable to avoid a hard landing,which may shorten a valve's life and generate unwanted noise. It ispreferable to achieve a valve landing speed less than 0.2 m/s. Thedetent force profile as a function of armature position is an actuatordesign parameter that can be altered by varying design aspects of theactuator, and needs to be taken into account when constructing a systemto land a valve with a certain velocity. For example, in the exemplaryoverhung actuator design shown in FIG. 5B, the actuator is constructedsuch that detent force is substantially zero during most of theexcursion range, and only starts taking effect when the armature isclose to its fully open (VFO) or fully closed (VFC) positions. When thevalve (armature) is close to the VFC position, the detent force acts tohold the valve in a closed position. The control current can beappropriately controlled (e.g., using velocity feedback) to provide aforce opposite to the detent force, to soft-seat the closure and helpachieve a desired valve landing velocity.

Referring again to FIG. 8, when the falling edge of the valve controlsignal is sensed by the downstream processor, it triggers the valveactuator to close at time T(4). In this regard, switching mechanism 603connects negative current control command 605 to PWM power module 502-1.The input voltage command 605 is synchronized with the falling edge ofthe valve timing signal, and causes the PWM power module to providenegative full current to the actuator, which causes the armature to movetowards a closed position. When the armature reaches a point where itsdistance and velocity satisfy a predetermined relationship at time T(5),switch mechanism 603 disables the negative full current command andconnects negative velocity feedback 601. Negative velocity feedbackgenerates a control current signal which in turn causes PWM power moduleto apply a current to the actuator with reverse polarity relative to thecurrent that was applied to move the valve towards its closed position,to reduce the velocity of the armature. The armature slows to a stop atits approximate desired displacement location (location (g) in thisexample) at time T(6), as the magnitude of the applied control currentis reduced to zero. At this time, similar to the case of a valve openingevent, a position servo control is activated (at time T(7)) to generatea current signal for fine-tuning the valve position, to try toaccurately land the valve at the desired position (i). But differentfrom a valve opening event, the position servo control for valve closingis deactivated when the valve is very close (h) to the desired position,where the detent force starts to take effect (for example, when thevalve is at −0.15 in position in FIG. 5B for the underhung design).

At this point, switch mechanism 603 again applies velocity feedbackcontrol. Velocity feedback is used to control the valve velocity when itis under the influence of detent forces. This ensures that the valve canbe made to land with a desired velocity. The actual landing velocity canbe controlled by adjusting parameters of the velocity feedback loop (byadding a constant offset, for example). The nature of negative velocityfeedback loop helps overcome the velocity fluctuations to maintain anapproximately constant landing velocity, until the valve actually landsat the desired position (i) at time T(8). Furthermore, for the exemplarydetent force profile, the detent force will hold the valve closed,without supplying additional control current once the valve has landed,to further provide power savings. It should be noted that depending onthe detent force profile, the detent force may not be sufficient to holdthe valve closed. In such a case, extra current may have to be suppliedto hold the valve closed.

It should be understood that a number of different operating conditions(such as a, b, c, d and T(0), T(1), T(2), T(3) etc. as shown in FIG. 8)could be defined for more sophisticated actuator control.

Other control strategies, which combine use of a velocity feedback loopto reduce valve speed, and a displacement loop for fine control ofpositioning, and that exploit of detent forces to save energy, arepossible. Performance criteria, such as rise time, overshoot,steady-state error and settling time, may be reasonably met by modifyingcontroller design and selection, including use of different controllerstructures such as PID, phase-lead, or phase-lag. More complicatedcontrollers such as a nonlinear dynamic controller or machine-learningbased controllers (e.g. neural network or fuzzy logic based controllers)may also be utilized.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the actuator does not have to be cylindrical on a plane aroundthe center axis, it could, instead, be a quadrilateral or a shapewithout planar symmetry around the center axis. Similarly, thedisplacement provided by the actuator does not have to be useful in adirection parallel to the center axis, but the displacement could betranslated to other directions. Specific numbers, arrangements andmagnetization of parts in all embodiments shown could also be modified.Additionally, an electromagnetic actuator designed in accordance withthis description may be used in a wide variety of application wherelinear actuation is desired and is not limited to engine valve control.

Accordingly, other embodiments are within the scope of the followingclaims.

1. An electromagnetic actuator, comprising: a stator assembly having aninner surface that defines an opening, the stator assembly comprising: acoiled conductor disposed near the inner surface of the stator assemblyand adapted to generate a first magnetic field when current is applied;a center pole formed of a material having high magnetic permeability,having a longitudinal axis, and defining a channel configured tocirculate cooling fluid; and an armature assembly at least partiallydisposed within the stator assembly opening, the armature assemblycomprising: a permanent magnet, wherein the armature assembly isconfigured to move in a direction parallel to the longitudinal axis ofthe center pole when current is applied to the coiled conductorassembly.
 2. An internal combustion engine comprising: a cylinder thatdefines a chamber; a valve adapted to control the flow of a liquid or agas into or out of the chamber; and an electromagnetic actuator coupledto the valve, the actuator comprising: a stator assembly comprising: acoiled conductor adapted to generate a first magnetic field when currentis applied; a center pole formed of a material having high magneticpermeability and having a longitudinal axis and a channel; and anarmature assembly at least partially disposed within the stator assemblyopening, the armature assembly comprising: a permanent magnet, whereinthe armature assembly is configured to move to open or close the valvewhen current is applied to the coiled conductor assembly, a coolingcircuit comprising: a heat exchanger; and a pump configured to circulatecooling fluid between the electromagnetic actuator and the heatexchanger through the channel in the center pole.
 3. Acomputer-implemented method for controlling an electromagnetic valveactuator having a stator that defines a longitudinal axis and anarmature disposed within the stator, the method comprising: receivinginformation about velocity and position of the valve; applying a controlsignal to the actuator by selectively activating a velocity feedbackloop and a position servo feedback loop to position the valve to adesired position.
 4. The method of claim 3 wherein the velocity feedbackloop reduces the valve velocity.
 5. The method of claim 3 wherein thedesired position is where the valve is fully opened.
 6. The method ofclaim 3 wherein the desired position is where the valve is fully closed.7. The method of claim 3 wherein the electromagnetic valve actuatorcomprises a stator assembly having an inner surface that defines anopening, the stator assembly comprising: a coiled conductor disposednear the inner surface of the stator assembly and adapted to generate afirst magnetic field when current is applied; a center pole formed of amaterial having high magnetic permeability and having a longitudinalaxis; and an armature assembly at least partially disposed within thestator assembly opening, the armature assembly comprising: a permanentmagnet, wherein the armature assembly is configured to move in adirection parallel to the longitudinal axis of the center pole whencurrent is applied to the coiled conductor assembly.
 8. The method ofclaim 3 wherein the actuator has a predetermined profile of detent forceversus actuator displacement, the method further comprising: activatingthe velocity feedback loop to compensate for the detent force at a givenarmature displacement.